1. Field of the Invention
Photodynamic therapy (PDT) is a medical technology which uses light energy in combination with photosensitizing agents to treat or detect pathologies of living tissue, including cancer and microbiological pathogens. Once pre-sensitized by the photosensitizing agent, the cancerous or abnormal cells can be detected by irradiation with light of an appropriate wavelength or waveband corresponding to an absorbing wavelength of the agent, with minimal damage to normal tissue. This procedure has been clinically used to detect a variety of cancers and tumors. Because PDT may be selective in detecting abnormal cells that have absorbed more of the agent, it can successfully be used to detect malignant tissue with less effect on surrounding benign tissue.
2. Brief Discussion of the Prior Art
Photodynamics provides a diagnosis tool that involves the use of a photosensitizing agent and a specific wavelength of light to detect tissue abnormalities. A photodynamic detection system consists of principal components: a photosensitizing agent, a light source (typically a laser), a light delivery means (typically optical fiber based); and a detection device. Two principal challenges for this emerging field of medicine are the development and validation of photosensitizer agents, and the development of reliable wavelength specific (laser) light sources at appropriate and convenient energy levels.
Photodynamic medical diagnosis entails the use of a photosensitizing agent that is relatively selectively concentrated in cancer cells or microbiological pathogen sites. Depending on the type of photosensitizer, it may be injected intravenously, ingested orally, or applied topically. After application of the photosensitizer, it is selectively retained by diseased tissue so that after a period of time, determined by the kinetics of the compound's distribution, there is more photosensitizer in the diseased tissue than in the normal tissue. The photosensitizer is then activated with a specific wavelength of light matching the absorption characteristics of the specific photosensitizer, typically using a laser.